kg to lbs divides the kilogram by 0.45359237. That number is the exact mass of the avoirdupois pound in kilograms, the pound used on bathroom scales and shipping labels, not a troy pound. One kilogram is therefore 1/0.45359237 pounds, which is 2.2046226218 lb to the digits this page keeps. Ten kilograms is 22.046226218 lb. Seventy kilograms, a common adult weight to use as a check, is 154.3235835 lb. The form opens on 1 kg to pounds so the first result is that 2.2046 figure and not a rounded 2.2. Swap the units for the other direction: one pound must come back as exactly 0.45359237 kg, which the page may display as 0.45359237.
The habit of saying 2.2 is why two calculators disagree by a third of a pound on a person and by several pounds on a shipment. 2.2 times 70 is 154. The defined conversion is 154.32. A clinic that records one decimal place in kilograms and a gym that records whole pounds are already rounding at different steps. Convert once, from the kilogram you were given, and round once at the end if the form demands a whole number. Do not convert to 2.2, round, and convert back. Ounces are in the same list: sixteen ounces to the pound, and the ounce mass is 0.028349523125 kg. Grams and milligrams are the decimal fractions of the kilogram. A tonne is 1000 kg. Stones are not listed. Divide pounds by 14 after you convert, if you actually need stones.
The BMI calculator uses this pound before it does anything else. If you type 154 lb and 5 feet 7 inches there, the weight it divides is 154 × 0.45359237 kilograms. Converting 154 lb on this page and typing the kilograms into the metric BMI form should land on the same index, within the one decimal the BMI page displays. If it does not, one of the heights was not 67 inches. The unit converter is this same mass list plus length, volume, temperature, speed, area, and bytes. This page only opens with kilograms and pounds selected, because that is the pair the title names.
Nothing is uploaded. There is no "ideal weight" attached to the result, and there should not be: a kilogram is a mass, not a verdict. If 1 lb does not return 0.45359237 kg, the factor in front of you is not this one.